Help Please with these​

Problem 17

Focus on one of the triangles. It has legs of 8 and 15. Use the pythagorean theorem to find the hypotenuse is 17.

Basically you're solving for c in a^2+b^2 = c^2. Use a = 8 and b = 15.

The diameter is 17 and the circumference is

C = pi*d = pi*17 = 17pi

Problem 18

This figure has four faces, so this is a tetrahedron. The "tetra" is greek that translates to "four".

Another possible name for this figure is triangular pyramid because we have a pyramid with a triangular base.